1. Field of the Invention
The present invention relates to a process and apparatus for the preparation of a sheet-shaped photoconductor that can be used fore various image guides or as a photoconductive material.
2. Description of the Related Art
A sheet-shaped photoconductor comprising optical fibers is used as an element of an image guide or a photoconductor for various display devices. As the process for continuously preparing this sheet-shaped photoconductor, there is known a process in which many optical fibers are arranged in the form of a sheet by a comb-like guide and piano wires and then are bonded and fixed, as disclosed in Japanese Examined Patent Publication No. 52-38419. If, however, the optical fibers are forcibly passed through the guide, the outer surfaces of the optical fibers are damaged and the optical properties are lowered. Moreover, since the bonding step is indispensable, the operation is complicated and the manufacturing cost is increased.
As a means for overcoming these problems, Japanese Unexamined Patent Publication No. 50-8540 proposes a process in which many optical fibers are melt-spun, and the spun optical fibers are fusion-bonded in parallel to one another while the as-spun fibers are maintained at a temperature higher than the glass transition temperature, whereby a tape-shaped photoconductor is prepared. According to this process, the post bonding treatment becomes unnecessary, but since the fibers are arranged in the form of a sheet by a rod-shaped width-regulating guide arranged downstream of a spinning nozzle, the optical fibers spun cylindrically and concentrically must be immediately linearly arranged in parallel to one another. Moreover, since this width-regulating guide has a rod-like shape, the difference of the yarn tension of optical fibers spun from the central portion of the spinning nozzle from that of optical fibers spun from the peripheral portion of the spinning nozzle is large, and therefore, it is difficult to stably guide the optical fibers. Accordingly, yarn unevenness occurs or an overlapping of the optical fibers occurs locally in the sheet-like arrangement of the optical fibers, with the result that it is difficult to obtain a sheet having a uniform width, and an optical fiber sheet not having uniform optical transmission characteristics is often formed.